High Availability (HA) cluster systems have been known as the technology for improving the reliability and availability of computers. In the HA cluster system, multiple servers are connected to each other to achieve the redundancy of the system.
In the HA cluster system, for example, the servers that constitute the HA cluster system are connected to each other via a dedicated network so that they monitor each other via the dedicated network to detect a failure. For example, in the HA cluster system, each server transmits, to a different server via a dedicated network, a signal called a heartbeat for externally notifying that it properly operates, and a different server monitors the signal to detect a failure. In the HA cluster system, if a stand-by server detects stoppage of a currently-operated server that performs processing in accordance with a processing request from a terminal apparatus or a failure during an operation, a switchover is made so that the stand-by server performs processing as a currently-operated apparatus; thus, processing is continuously performed while a failure occurs.
[Patent Literature 1] Japanese Laid-open Patent Publication No. 2008-305353
Furthermore, in the HA cluster system, even if a failure occurs in a server, a heartbeat communication sometimes continues. For example, because of a high reliability of an operating system (OS), even if part of the OS does not operate, the overall server can operate. Therefore, in some cases, when a failure occurs in part of the OS, the heartbeat properly operates in the server while processing of the application does not properly operate.
For this reason, in the HA cluster system, for example, it is possible that a terminal apparatus also monitors a server and, when detecting a failure, switches a currently-operated apparatus.
However, if the terminal apparatus transmits a switch command, there is a possibility that a switch command statement is intercepted by a malicious user and the command statement is leaked. If the command statement is leaked as described above, there is a possibility of hacking of the system.